Land-dwelling leeches can seem like peaceful creatures. But be careful when they’re out for blood.
A thirst for blood may have led to acts of surprising athleticism, as documented in a pair of videos released Thursday by two scientists alongside a study in the journal Biotropica. In each, a brown pillar of flesh and muscle, atop a green leaf, swings back and forth in its search for blood. Then it rolls itself up into a comma and bundles the bottom half of it. Finally, the leech leaps and flies through the air with a kind of wild abandon.
Lean closer, come to your ear: you can almost imagine yourself letting out a little “Yahooooooo!”
Mai Fahmy, currently a postdoctoral researcher at Fordham University and a visiting scholar at the American Museum of Natural History, made the first video in Madagascar in 2017. At the time, she had never heard of the long-running debate among scientists about whether leeches could jump.
“It takes a few years of researching leeches before you learn anything about the great debate,” says Michael Tessler, a specialist in leech biology at Medgar Evers College of the City University of New York and a research associate at the natural history museum. He is the co-author of Dr. Fahmy.
Her 10-second video, taken on a whim, turned out to be the first recorded visual evidence of leeches jumping known to science.
There were other claims about jumping leeches. In 1881, the biologist Ernst Haeckel visited Sri Lanka and described the behavior: Not only did they crawl on the ground, he wrote, but they could also ‘jump to reach their victim’.
Scientists have long been skeptical of such anecdotal evidence. In tropical forests it is common to discover leeches unexpectedly high on the body, on the arms, neck, shoulder or even in the eyes. Did observers find leeches that had fallen from vegetation and assume the creatures could jump?
After Dr. Fahmy shared her first jumping leech video with other people, most of them immediately recognized the jump. When she and Dr. Tessler analyzed the leech’s movement, they found that it made a curling motion, similar to the motion a cobra makes before striking. The gesture seems to be a collection of energy, a preparation for what comes next: flight and an uncoordinated, almost slapstick landing.
In fact, they found that this particular sequence of movements – curling up, jumping, ending with a belly flop – is not uncommon in other worm-like organisms that jump, including caterpillars and fly larvae.
The way the leech in the 2017 video plops onto the forest floor, with very little apparent control over its landing, appears to be common among these creatures. It is possible, said Dr. Tessler, that because larvae, caterpillars and leeches are very light, they do not require a precise landing to avoid injury.
In 2023, Dr. Fahmy again in Madagascar and she took out her phone to film some leeches on a leaf. Within seconds, she saw the same movement again: one of the leeches gathered together and flew into the air. She and Dr. Tessler identified the leech species in both videos as Chtonobdella fallax, a member of a larger family also found in the Seychelles, Southeast Asia and the South Pacific Islands..
That Dr. Fahmy was able to create these videos without much planning, suggesting that jumping is normal behavior for some leeches. The researchers hope that other people will film more acrobatic bloodsuckers. It may be that one of the problems that hindered the identification of jumping leeches all these years was the absence of people with cameras.
Dr. Fahmy and Dr. However, Tessler notes that the presence of a large, warm pocket of blood nearby can make leeches quite excited. They will start the leech version of running, a furious inchworming past, to try to get closer to you.
“That can be quite hectic,” said Dr. Fahmy. “And when there are a lot of leeches, it can be quite overwhelming in the field to find yourself being so intensely chased by so many little guys.”
“They’re booking it,” Dr. added. Tessler added. “It can be pretty wild.”